Gasthermen are devices used for heating water in residential and commercial settings. They work by burning gas to heat the water, which is then circulated through pipes to provide hot water for various uses, such as showers, sinks, and heating systems. These appliances are typically more energy-efficient than traditional water heaters, as they heat water on demand rather than storing it. Gasthermen come in various sizes and types, including tankless models, which provide continuous hot water without the need for a storage tank.